Fiber finishes having hydrophobic organic ester components, with a melting point lower than ambient temperature, have been used by fiber producers because of their ease of handling at ambient temperature. These liquid esters provide lubrication to the fiber during spinning, plying, twisting, and fabric weaving operations. Unfortunately, these liquid lubricants tend to promote excessive stiffness in resorcinol-formaldehyde-latex (RFL) treated cords. This stiffness causes handling problems in tire manufacturing and it is accompanied by low air permeability of RFL dipped cord which causes excessive curing blows in tires.
Triglyceride ester lubricants used in commercial finishes are examples of stiffness-promoting finish ingredients. Examples of such esters are transesterified triglyceride made from glyceryl trioleate, coconut oil and palm oil and having a melting point of approximately 21.degree. C. and coconut oil with a melting point of approximately 24.degree.-27.degree. C.
It is especially important for tire cords not to have excessive stiffness or poor air permeability, the cause of which is believed to be excessive dip penetration into the tire cord. The object of this invention is to develop a tire yarn convertible to a tire cord, said cord having low stiffness and high air permeability and a process for making such tire yarn.
High dipped cord stiffness can be reduced by mechanically exercising fabrics during the fabric hot stretching process. For example, fabrics can be passed over breaker or flexing bars under relatively high tensions to physically break apart stuck filaments to reduce dipped cord stiffness. However , this is undesirable in that some dip is removed and fabrics may be damaged. Furthermore, mechanical fabric treatments do not increase dipped cord permeability.
Fabric hot stretching temperatures and tensions can influence dipped cord air permeability, but it is difficult to significantly increase air permeability without adversely affecting other properties such as adhesion. Curing blows caused by low air permeability dipped cords can be reduced by using lower temperature, longer tire curing cycles, but this increases tire manufacturing cost.
Excessive dipped cord stiffness can cause several problems in tire building, including difficulty in making tight uniform turn-ups and excessive trapped air which aggravates curing blows in tires. It is physically more difficult to turn carcass fabric plies around the bead, causing operator discomfort. Even when plies are turned up automatically, there is a tendency for turn-ups to come loose. Low air permeability leads to excessive curing blows in tires. Invariably some air is trapped between components as tires are assembled. If this air collects in pockets during the tire curing process, air bubbles result in the cured tire, and the tire must be rejected.